1. Field of the Invention
The present invention relates to a dual fuel engine capable of running on either gas fuel or liquid fuel by the selection of an operation mode.
2. Description of the Related Art
Conventionally, what is known as a xe2x80x98dual fuel enginexe2x80x99, which is capable of operating using both a gas operation mode, in which a gas fuel is used, and a diesel operation mode, in which a liquid fuel is used, is known as an engine that drives a power generator. An example of this engine is one that switches between operation modes and when in gas operation mode operates by combusting a vapor fuel using a liquid fuel injection valve provided in the center of the cylinder head, with a small quantity of pilot fuel oil (a liquid fuel of approximately 5-15% of the total heat quantity) as an ignition source. When in diesel operation mode, this engine is able to operate by combusting 100% liquid fuel using the liquid fuel injection valve.
In this dual fuel engine, because the compression ratio is lowered in comparison to a diesel engine in order to avoid knocking when in gas operation mode, compression ignition of the pilot fuel oil at startup is difficult. Therefore, when in gas operation mode, a liquid fuel having a high ignitability is used as the pilot fuel to aid the ignition of the vapor fuel, which has a low ignitability. Specifically, the engine is first started up using a liquid fuel that has excellent ignitability and is then run until it is warmed up. When the engine has warmed up and the engine operation load ratio is approximately 30% or greater, the fuel is switched from a liquid fuel to a gas fuel.
In the aforementioned conventional engine, as a result of combusting a liquid fuel of approximately 5-15% of the total heat quantity as pilot fuel oil in gas operation mode, it is not possible to meet the regulation values for NOx and soot that are applied to gas engines. In order to reduce NOx and soot, it is possible to ignite and combust gas fuel alone by using an ignition plug or a glow plug instead of using this pilot fuel oil ignition method. However, in this case, a pilot fuel injection valve for vapor fuel is needed in addition to the liquid fuel injection valve, resulting in problems arising such as the engine structure becoming complicated, and the number of parts as well as the engine manufacturing costs increasing.
Moreover, in gas operation mode, because startup by compression ignition of the pilot fuel oil is difficult and requires the engine to be warmed up as described above, it is not possible to start the engine quickly. Moreover, because the compression ratio is set low, the problems arise that thermal efficiency at low load is deteriorated and the stability of the combustion does not improve.
Furthermore, in diesel mode operation, high combustion efficiency can be obtained by directly injecting liquid fuel into the main combustion chamber and combusting it. However, the NOx value in the exhaust gas is then high giving rise to the problems of it not being possible to meet exhaust gas regulation values, which are expected to be consolidated even further in future, and an after treatment by a NOx removal system becoming necessary. Consequently, installation costs are very high.
The present invention was conceived in view of the above circumstances and it is an object thereof to provide a dual fuel engine that allows an arbitrary selection to be made between gas operation and diesel operation, that enables regular electric power generation to be performed by gas operation and emergency electric power generation to be performed by diesel operation, and that, in addition, achieves a reduction in NOx even when in diesel operation.
A further object of the present invention is to provide a dual fuel engine that allows adjustments and alterations to be made in the compression ratio of a vapor compressed in a cylinder in accordance with the operating state of the engine, that can be started quickly even when in gas operation, and that makes operations at a high combustion efficiency possible over the entire load range.
In order to solve the above described problems, the present invention is characterized by the following points.
Namely, the first invention of the present invention is a dual fuel engine that provides drive output by combusting, in a main combustion chamber partitioned by a cylinder, by a piston that moves reciprocally inside this cylinder, and by a cylinder head having an intake port provided with an intake valve and an exhaust port provided with an exhaust valve, one of either a gas fuel or a liquid fuel together with a gas compressed by the piston in accordance with an operation mode, wherein the dual fuel engine is provided with a precombustion chamber unit, which is located in the cylinder head of the dual fuel gas engine, having a precombustion chamber that has a liquid fuel injection valve and that combusts liquid fuel injected from this liquid fuel injection valve together with the compressed gas, and wherein the dual fuel engine is also provided with a compression ratio control valve that is located in an air passage that connects the main combustion chamber with the exterior of the main combustion chamber and that varies the compression ratio of the gas in an initial stage of compression of the gas by the piston by opening and closing the air passage so as to allow a portion of the compressed gas to escape to the air passage, and with a fuel gas feeding apparatus that feeds gas fuel to the main combustion chamber.
In the above described dual fuel engine, in gas operation mode a fuel air mixture formed by mixing gas fuel from the fuel gas feeding apparatus with air from an intake port is fed to the main combustion chamber and compressed by a piston stroke. A portion of this compressed fuel air mixture enters into the precombustion chamber of the precombustion chamber unit and is ignited by an extremely small pilot quantity of liquid fuel injected from the liquid fuel injection valve. The remainder of the fuel air mixture inside the main combustion chamber is then combusted by this ignited flame. Moreover, in the initial stages of the compression of the air fuel mixture by the piston, the air passage is opened and closed by the compression ratio control valve and a portion of the compressed fuel air mixture escapes from the main combustion chamber via the air passage so that the compression ratio of the fuel air mixture inside the main combustion chamber is able to be changed.
In diesel operation mode, the feeding of gas fuel from the fuel gas feeding apparatus is cut off and the air passage is closed by the compression ratio control valve. Air fed from the intake port to the main combustion chamber is compressed by the piston to a compression ratio suitable for diesel operation. 100% of the liquid fuel injected from the liquid fuel injection valve is ignited in the precombustion chamber by this compressed air and is combusted.
According to this dual fuel engine, when in gas operation mode, by opening and closing the air passage connecting the main combustion chamber with the outside thereof using the compression ratio control valve, the compression ratio of the gas air mixture introduced into the main combustion chamber is able to be changed. As a result, by adjusting the compression ratio as is appropriate in accordance with the operating state, such as whether the engine is being started up, is running at low load, or is running at high load, compression ignition of the liquid fuel at startup can be achieved without using an ignition device such as an ignition plug, and the engine can be started without being warmed up. Furthermore, by setting the compression ratio at the same level as for diesel operation even in the low load range, thermal efficiency and combustion stability is improved. Accordingly, a high thermal efficiency over the entire load range can be obtained.
In diesel operation mode, because 100% of the liquid, fuel injected from the liquid fuel injection valve is combusted using a precombustion method in which the liquid fuel is ignited in a precombustion chamber, the engine can be run with the NOx discharge density comparatively suppressed.
Consequently, according to this dual fuel engine, a single engine can be used to the power generator which is normally operated by the gas operation mode in which full advantage is taken of the low pollution properties of gas fuel, and is also operated by the diesel operation mode in emergencies as a disaster prevention power source and the like.
The second invention of the present invention is the dual fuel engine according to the above first invention, wherein, in gas operation mode, by altering opening and closing timings of the air passage in accordance with an operation state such as engine startup, low load operation, or high load operation, the compression ratio control valve adjusts the compression ratio by raising it for startup and low load operation and lowering it for high load operation.
In this dual fuel engine, in gas operation mode, because the compression ratio of the gas air mixture inside the main combustion chamber is high at startup and when the engine is operating at a low load, compression ignition of the slight pilot quantity of liquid fuel injected into the precombustion chamber from the liquid fuel injection valve can be performed reliably without using an ignition device. As a result, startup of the engine is simple and combustion efficiency and combustion stability are improved. Moreover, when operating at a high load, because the compression ratio of the air fuel mixture is low, knocking can be avoided and stable combustion can be achieved. Furthermore, even during combustion generated by compression ignition of liquid fuel, because the injection amount is extremely slight, the discharge density of NOx and soot can be kept at an extremely low level.
The third invention of the present invention is the dual fuel engine according to the second invention, wherein opening and closing timings of the compression ratio control valve are set such that the valve is opened at a start time of a compression stroke of the gas by the piston, and the valve is closed when a predetermined crankshaft rotation angle is reached with the engine crankshaft rotation angle at the start time of the compression stroke taken as a reference.
In this dual fuel engine, because the opening and closing timings of the compression ratio control valve are set based on the engine crankshaft rotation angle, the compression ratio of the gas in the main combustion chamber when in gas operation mode is set accurately for the operating load.
The fourth invention of the present invention is the dual fuel engine according to any one of the first to third inventions, wherein the fuel gas feeding apparatus is provided with a gas feeding pipe that is connected to the intake port, an electromagnetic valve that adjusts a feeding quantity of gas fuel from a gas fuel source to the gas feeding pipe, and an electromagnetic valve driver that drives the electromagnetic valve to open and close by speed governing control, and wherein injection of a pilot quantity of liquid fuel by the liquid fuel injection valve and injection of liquid fuel by speed governing control are possible, and, moreover, wherein the compression ratio control valve is operated by an electromagnetic coil with adjustment of a valve opening time from when the valve is opened so as to communicate the main combustion chamber with the air passage until the valve is closed so as to shut off this communication being possible in accordance with an operating state of the engine, and, furthermore, wherein a control apparatus that operates each is connected to the electromagnetic valve driver, the liquid fuel injection valve, and the electromagnetic coil, and this control apparatus operates by selection of the operation mode and when in gas operation operates the electromagnetic valve driver by speed governing control such that the electromagnetic valve is opened and closed, and operates the liquid fuel injection valve to cause it to inject a pilot quantity of liquid fuel, and also operates the electromagnetic coil such that the valve opening time of the compression ratio control valve is adjusted in accordance with the operating state of the engine, while in diesel operation mode operates the electromagnetic valve driver such that the electromagnetic valve is closed, and operates the liquid fuel injection valve such that injection of liquid fuel by speed governing control is performed, and also operates the electromagnetic coil such that the compression ratio control valve is closed.
In this dual fuel engine, when in gas operation mode, the electromagnetic valve driver opens and closes the electromagnetic valve using speed governing control based on operation commands from the control apparatus. Gas fuel is fed as the main fuel to the interior of the main combustion chamber and the fuel injection valve injects a pilot quantity of liquid fuel. In addition, the electromagnetic coil adjusts the valve opening timings of the compression ratio control valve in accordance with the operating state of the engine. As a result, because the valve open time of the compression ratio control valve is shortened and the compression ratio of the air gas mixture inside the main combustion chamber is raised at engine startup or when the engine is operating at low load, compression ignition of the pilot quantity of liquid fuel injected from the liquid fuel injection valve is simplified, and an engine can be started without it depending on the engine being warmed up. Moreover, not only is an operation with excellent combustion efficiency made possible, but because at high load the valve open time of the compression ratio control valve is shortened and the compression ratio of the air gas mixture reduced, knocking is also reliably prevented from being generated and stable operation is made possible.
Moreover, when in diesel operation mode, based on an operation command from the control apparatus, the electromagnetic valve driver closes the electromagnetic valve. The liquid fuel injection valve injects liquid fuel into the precombustion chamber using speed governing control, and the electromagnetic coil closes the compression ratio control valve. As a result, the compression ratio of the air inside the main combustion chamber is raised and liquid fuel is combusted as the main fuel by a precombustion method. This enables NOx in the exhaust gas to be reduced when the engine is in operation.
The fifth invention of the present invention is the dual fuel engine according to the above described first to fourth inventions, wherein the air passage is connected to the intake port.
In this dual fuel engine, because a portion of the air gas mixture introduced into the main combustion chamber is returned to the intake port, gas fuel is not wasted and is used effectively.
The sixth invention of the present invention is the dual fuel engine according to the above described first to fifth inventions, wherein the air passage is connected to an insert intake manifold of an exhaust turbocharger that is driven by exhaust gas from the exhaust port and feeds compressed air to the intake port.
In this dual fuel engine, because a portion of the air gas mixture introduced into the combustion chamber is blown onto the impeller of a compressor in the an exhaust turbocharger, the transient response performance of the exhaust turbocharger is improved and, in low load regions, the exhaust temperature is raised and quantity of black smoke that is output is reduced.